In general, a rechargeable Ni/MH secondary battery consists of a MH anode, 6M KOH electrolyte and a Ni(OH).sub.2 cathode, and the activation of a Ni-MH secondary battery depends on a MH anode, since the activation of a cathode is performed more easily than that of an anode in the Ni/MH secondary battery. When metal hydride(MH) alloy constituting an anode is exposed to the air, oxidized membrane is formed on the surface of the MH alloy, which results in no absorption of hydrogen during hydrogenation reaction. A process for treating the hydrogen-absorbing alloy in such a condition to absorb and release hydrogen easily is called "activation treatment". The method of activation treatment employed depends on the kind of MH, and the ease of the activation treatment is also dependent on the same.
An alloy of AB.sub.2 type-Laves phase(A: an element having high affinity for hydrogen, B: transition metal), has a hydrogen-absorbing capacity higher than commercially available alloys of AB.sub.5 type and has a long life span in an electrolyte, which allows the alloy to attract attention as a material for an anode employed in Ni/MH secondary battery. However, its activation during the construction process of an electrode is so difficult that it cannot be practically applied in the industry.
On the other hand, in order to improve the activation characteristics of the hydrogen-absorbing alloy of AB.sub.2 type, a variety of studies on the design and surface treatment of the alloy have been carried out in the art:
Concerning the method of adding/replacing elements during the preparation of an alloy, Kim et al. reported that the addition of small amounts of rare-earth elements (La, Mm, Nd) to a ZrCrNi alloy results in reducing the number of charge/discharge cycle from 20 cycles to 5 cycles or less (see: Kim, S. R. et al., J. Alloys Comp., 185:L1(1992)), and Sawa et al. reported that the substitution of Zr with Ti in a Zr--Ni alloy system leads to improved activation characteristics (see: Sawa, H. et al., Zeit. fur Phys. Chem., 164:1527(1989)).
Concerning the method of surface treatment after the preparation of an electrode, Wakao et al. reported that the immersion of an electrode made of a Zr--V--Ni alloy in a KOH solution leads to efficient activation of alloy in a manner that the activation can be performed within about 5 cycles, and more efficient activation can be realized under a condition of long immersion time, high immersion temperature and anodic oxidation treatment(see: Wakao H. et al., "Int. Symp. on Metal Hydrogen Systems", September, 1990). Also, Lee et al. reported that the immersion of a ZrCr.sub.0.8 Ni.sub.1.2 alloy in a solution containing NaBH.sub.4 leads to a remarkably efficient activation within 2-3 cycles in half cell grounded on the hydrogen absorption by chemical reaction and surface change as well, and the immersion in a HF+HNO.sub.3 solution or in a KOH solution complete the activation within 10 cycles (see: J. H. Lee, Ph.D. Thesis, KAIST(1993)).
On the other hand, the previous studies on the improvement of electrode activation characteristics by immersing an electrode in KOH, HF+H.sub.2 O.sub.2 and NaBH.sub.4, etc., have revealed that the activation process is realized by following two steps: first, an electrode is immersed in an immersion solution for a while; secondly, charge/discharge cycling is carried out in an electrolyte after the immersion.